Why are stages upside down?

[guitarxe]

In the game, the top stage is 0, and increases in number as you go down. But when I see diagrams of any real life rockets, the bottom-most stage is number 1, and increases in number as you go up.

Why this flip?

Edited September 17, 2014 by guitarxe
change to answered

[Moonfrog]

Basically its a preference. It should be done top stage as 0 then work downwards. In the same way as you would say T minus 5 minutes. Not just say 5 minutes untill launch. I would imagine professionals start at 0, when your not and you look at the rocket, the first stage that fires, you naturally assume is the first stage. When building a rocket, the 1st stage is the smallest stage usually at the top, then u build the 2nd and join them together, etc.

Its basically a mix up. From what i can tell, i could be wrong.

[Rhomphaia]

I am guessing that since you build from the top down, staging order is reversed from the norm so that the stages don't have to be re-numbered every time you add a new one to the bottom.

[cantab]

At one point you had to start building your rocket with a command pod, and thus normally design it from the top down. Even though it's no longer obligatory that's still the most popular way to do things and has advantages. With that in mind, it makes sense to make the first stage placed be the lowest numbered and the last stage fired.

[Red Iron Crown]

It does go against the convention in real rocketry, though. Probably just convenient programming-wise.

[Pecan]

I suspect it was an old design-decision that made sense at the time (and might still make sense internally) but, yes, it can be confusing.

[Kasuha]

It relieves the game from remembering what stage number is your command pod. The last thing to stay is always stage 0, regardless, of how many stages you dropped while getting to that state.

Imagine you have a 5-stage rocket, spend two stages getting it to orbit, then build another 5-stage rocket, get it to orbit as well, and dock with the first rocket making it into another 5-stage rocket. How should these stages be numbered? If the game had to remember them, it would be 5-4-(3/5)-4-3. That does not look pretty.

You'd likely also not like if your first stage to drop was always stage 0. The way it is implemented, stages keep their numbers as long as you don't start doing funny things.

[Srpadget]

What everyone else has said already about history and programming convenience.

Also, it's not a KSP-specific programming convention. Professional-grade rocket/missile trajectory simulators (at least the ones I've worked with, to the best of my recollection) all use the same sort of stage numbering: start at 0 or 1 for the final payload, and increment stage number in reverse order of separation (so the highest-numbered stage is the first section to get dropped on the way up).